1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
Various versions of fuel injection valves of the type with which this invention is concerned are known from the prior art. For instance, in German Patent Disclosure DE 196 50 865 A1, a fuel injection valve is described that is in constant communication with a common rail in which fuel at high pressure is furnished. The fuel injection valve has a housing in which a valve member is disposed longitudinally displaceably in a bore; by its longitudinal motion, this valve member controls the opening of at least one injection opening, through which fuel from a pressure chamber surrounding the valve member is injected into the combustion chamber of the engine. Because of the very fast closing events of the valve member, which are completed within a range of only a few milliseconds, pressure fluctuations occur in the pressure chamber both upon opening and upon closure of the fuel injection valve and lead on the one hand to severe mechanical stresses on the housing and on the other to an indefinite pressure state at the injection openings at the beginning of the next injection, so that the following injection begins at a state that is not precisely defined, making accurate metering and an accurate instant of injection impossible. Especially in injection events that are broken down into a preinjection, main injection and/or postinjection, this is a problem, since modern fuel injection systems react very sensitively to fluctuations in quantity upon injection.
Also known from the prior art are fuel injection valves of the kind shown for instance in German Patent Disclosure DE 196 18 650 A1. In such a fuel injection valve, there is also a housing, in which a pistonlike valve member is disposed longitudinally displaceably with a bore; with its end toward the combustion chamber, this valve member controls the opening of at least one injection opening. The valve member is again surrounded by a pressure chamber, which by the longitudinal motion of the valve member can be made to communicate with the injection openings. Via an inlet conduit extending in the housing, the pressure chamber communicates with a high-pressure fuel source, by which fuel at high pressure can be delivered to the pressure chamber. The valve member is urged in the closing direction with a closing force by a mechanical device in the housing of the fuel injection valve, preferably by a helical compression spring, so that in the absence of a corresponding hydraulic opposing force, it remains in the closing position and thus closes the injection openings. In this fuel injection valve as well, especially at the onset and end of the injection event, pressure fluctuations occur in the region of the pressure chamber, where they can lead to mechanical stresses, and if the fluctuations persist can lead to an undefined state at the onset of the next injection and can impair the quality of subsequent injections.